* [PATCH v2 0/2] rcu: Make rcu_normal_after_boot writable again
@ 2021-08-10 8:48 Juri Lelli
2021-08-10 8:48 ` [PATCH v2 1/2] " Juri Lelli
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: Juri Lelli @ 2021-08-10 8:48 UTC (permalink / raw)
To: paulmck, josh
Cc: linux-kernel, linux-rt-users, peterz, bigeasy, tglx, rostedt,
mathieu.desnoyers, jiangshanlai, joel, rcu, Juri Lelli
Hi,
v2 of a proposed RCU change to make rcu_normal_after_boot feature usable
on PREEMPT_RT as well, as it turns out it's useful on RT as well on
NO_HZ_FULL configurations.
v2 gained an additional patch to revise rcu update module parameters
permissions (as suggested during v1 review [1]).
Changes wrt v1:
- Restrict the option to !PREEMPT_RT || NO_HZ_FULL (Paul, Sebastian)
- Change module params permissions (Paul) (02/02)
Thanks,
Juri
v1 - https://lore.kernel.org/lkml/20210805080123.16320-1-juri.lelli@redhat.com/
Juri Lelli (2):
rcu: Make rcu_normal_after_boot writable again
rcu: Make rcu update module parameters world-readable
kernel/rcu/tree_exp.h | 1 -
kernel/rcu/update.c | 8 ++++----
2 files changed, 4 insertions(+), 5 deletions(-)
--
2.31.1
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH v2 1/2] rcu: Make rcu_normal_after_boot writable again
2021-08-10 8:48 [PATCH v2 0/2] rcu: Make rcu_normal_after_boot writable again Juri Lelli
@ 2021-08-10 8:48 ` Juri Lelli
2021-08-10 8:48 ` [PATCH v2 2/2] rcu: Make rcu update module parameters world-readable Juri Lelli
2021-08-10 18:41 ` [PATCH v2 0/2] rcu: Make rcu_normal_after_boot writable again Paul E. McKenney
2 siblings, 0 replies; 4+ messages in thread
From: Juri Lelli @ 2021-08-10 8:48 UTC (permalink / raw)
To: paulmck, josh
Cc: linux-kernel, linux-rt-users, peterz, bigeasy, tglx, rostedt,
mathieu.desnoyers, jiangshanlai, joel, rcu, Juri Lelli
Certain configurations (e.g., systems that make heavy use of netns)
need to use synchronize_rcu_expedited() to service RCU grace periods
even after boot.
Even though synchronize_rcu_expedited() has been traditionally
considered harmful for RT for the heavy use of IPIs, it is perfectly
usable under certain conditions (e.g. nohz_full).
Make rcupdate.rcu_normal_after_boot= again writeable on RT (if NO_HZ_
FULL is defined), but keep its default value to 1 (enabled) to avoid
regressions. Users who need synchronize_rcu_expedited() will boot with
rcupdate.rcu_normal_after_ boot=0 in the kernel cmdline.
Reflect the change in synchronize_rcu_expedited_wait() by removing the
WARN related to CONFIG_PREEMPT_RT.
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
---
kernel/rcu/tree_exp.h | 1 -
kernel/rcu/update.c | 2 +-
2 files changed, 1 insertion(+), 2 deletions(-)
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 2796084ef85a..d9e4f8eb9ae2 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -512,7 +512,6 @@ static void synchronize_rcu_expedited_wait(void)
j = READ_ONCE(jiffies_till_first_fqs);
if (synchronize_rcu_expedited_wait_once(j + HZ))
return;
- WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_RT));
}
for (;;) {
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index c21b38cc25e9..bd551134e2f4 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -57,7 +57,7 @@
module_param(rcu_expedited, int, 0);
module_param(rcu_normal, int, 0);
static int rcu_normal_after_boot = IS_ENABLED(CONFIG_PREEMPT_RT);
-#ifndef CONFIG_PREEMPT_RT
+#if !defined(CONFIG_PREEMPT_RT) || defined(CONFIG_NO_HZ_FULL)
module_param(rcu_normal_after_boot, int, 0);
#endif
#endif /* #ifndef CONFIG_TINY_RCU */
--
2.31.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* [PATCH v2 2/2] rcu: Make rcu update module parameters world-readable
2021-08-10 8:48 [PATCH v2 0/2] rcu: Make rcu_normal_after_boot writable again Juri Lelli
2021-08-10 8:48 ` [PATCH v2 1/2] " Juri Lelli
@ 2021-08-10 8:48 ` Juri Lelli
2021-08-10 18:41 ` [PATCH v2 0/2] rcu: Make rcu_normal_after_boot writable again Paul E. McKenney
2 siblings, 0 replies; 4+ messages in thread
From: Juri Lelli @ 2021-08-10 8:48 UTC (permalink / raw)
To: paulmck, josh
Cc: linux-kernel, linux-rt-users, peterz, bigeasy, tglx, rostedt,
mathieu.desnoyers, jiangshanlai, joel, rcu, Juri Lelli
rcu update module parameters currently don't appear in sysfs and this is
a serviceability issue as it might be needed to access their default
values at runtime.
Fix this issue by changing rcu update module parameters permissions to
world-readable.
Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
---
kernel/rcu/update.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index bd551134e2f4..94282dc12bab 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -54,11 +54,11 @@
#define MODULE_PARAM_PREFIX "rcupdate."
#ifndef CONFIG_TINY_RCU
-module_param(rcu_expedited, int, 0);
-module_param(rcu_normal, int, 0);
+module_param(rcu_expedited, int, 0444);
+module_param(rcu_normal, int, 0444);
static int rcu_normal_after_boot = IS_ENABLED(CONFIG_PREEMPT_RT);
#if !defined(CONFIG_PREEMPT_RT) || defined(CONFIG_NO_HZ_FULL)
-module_param(rcu_normal_after_boot, int, 0);
+module_param(rcu_normal_after_boot, int, 0444);
#endif
#endif /* #ifndef CONFIG_TINY_RCU */
--
2.31.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v2 0/2] rcu: Make rcu_normal_after_boot writable again
2021-08-10 8:48 [PATCH v2 0/2] rcu: Make rcu_normal_after_boot writable again Juri Lelli
2021-08-10 8:48 ` [PATCH v2 1/2] " Juri Lelli
2021-08-10 8:48 ` [PATCH v2 2/2] rcu: Make rcu update module parameters world-readable Juri Lelli
@ 2021-08-10 18:41 ` Paul E. McKenney
2 siblings, 0 replies; 4+ messages in thread
From: Paul E. McKenney @ 2021-08-10 18:41 UTC (permalink / raw)
To: Juri Lelli
Cc: josh, linux-kernel, linux-rt-users, peterz, bigeasy, tglx,
rostedt, mathieu.desnoyers, jiangshanlai, joel, rcu
On Tue, Aug 10, 2021 at 10:48:14AM +0200, Juri Lelli wrote:
> Hi,
>
> v2 of a proposed RCU change to make rcu_normal_after_boot feature usable
> on PREEMPT_RT as well, as it turns out it's useful on RT as well on
> NO_HZ_FULL configurations.
>
> v2 gained an additional patch to revise rcu update module parameters
> permissions (as suggested during v1 review [1]).
Queued and pushed, thank you!
Thanx, Paul
> Changes wrt v1:
>
> - Restrict the option to !PREEMPT_RT || NO_HZ_FULL (Paul, Sebastian)
> - Change module params permissions (Paul) (02/02)
>
> Thanks,
> Juri
>
> v1 - https://lore.kernel.org/lkml/20210805080123.16320-1-juri.lelli@redhat.com/
>
> Juri Lelli (2):
> rcu: Make rcu_normal_after_boot writable again
> rcu: Make rcu update module parameters world-readable
>
> kernel/rcu/tree_exp.h | 1 -
> kernel/rcu/update.c | 8 ++++----
> 2 files changed, 4 insertions(+), 5 deletions(-)
>
> --
> 2.31.1
>
^ permalink raw reply [flat|nested] 4+ messages in thread
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2021-08-10 8:48 [PATCH v2 0/2] rcu: Make rcu_normal_after_boot writable again Juri Lelli
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2021-08-10 8:48 ` [PATCH v2 2/2] rcu: Make rcu update module parameters world-readable Juri Lelli
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